Light detecting device

ABSTRACT

In a photodetecting device  3,  positional alignment marks  18 A,  18 B to serve as positional references of a photodetecting element  11  are formed at the front surface side of the photodetecting element  11.  Moreover, a pin base  13  is provided with a threaded fitting pin  32  to be fitted with a cold plate  2,  and the threaded fitting pin  32  is accurately positionally aligned with respect to the photodetecting element  11  via a positioning portion  33  positioned with respect to the positional alignment marks  18 A,  18 B exposed from a slit portion  23  and a cutaway portion  24  of a wiring board  12.  Accordingly, in the photodetecting device  3,  by only fitting the threaded fitting pin  32  with a recess portion  4  of the cold plate  2,  the photodetecting element  11  is accurately positionally aligned with respect to the cold plate  2.

TECHNICAL FIELD

The present invention relates to a photodetecting device with aso-called back-incident type photodetecting element.

BACKGROUND ART

Conventionally, so-called back-incident type photodetecting elementshave been known. This type of photodetecting element is provided with alight-incident surface at the back surface side of a semiconductorsubstrate, and detects light made incident from the light-incidentsurface by a photodetecting section being at the front surface side. Asa photodetecting device with such a photodetecting element, there isprovided, for example, a semiconductor energy detector described inPatent Document 1. This semiconductor energy detector includes a BT-CCD(Back-Thinned CCD) for which a part of the semiconductor substrate isthinned on the opposite side to the photodetecting section and which iscapable of detecting various types of energy beams including ultravioletrays, soft X-rays, and electron beams at a high sensitivity, and usedas, for example, a photodetecting section of a telescope forastronomical observation.

Patent Document 1: Japanese Published Unexamined Patent Application No.H06-196680

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

In such a telescope application etc., as described above, for providingthe photodetecting section with a large area, it is effective to adopt aso-called buttable arrangement structure, where a plurality ofphotodetecting devices are disposed in a matrix arrangement on aninstallation body such as a cold plate. In such an arrangementstructure, suppressing the interval between the respectivephotodetecting devices to, for example, 100 μm or less makes it possibleto arrange the photodetecting devices at a high density, while requiredis a high degree of positional alignment accuracy of photodetectingelements with respect to the installation body.

The present invention has been made in order to solve the aboveproblems, and an object thereof is to provide a photodetecting devicecapable of accurately performing positional alignment of thephotodetecting element with respect to the installation body.

Means for Solving the Problem

In order to solve the above problems, a photodetecting device accordingto the present invention includes: a photodetecting element that detectslight made incident from one surface by a photodetecting section beingon a side of the other surface; a wiring board provided at the otherside of the photodetecting element and electrically connected with thephotodetecting section; and a base provided at the other side of thewiring board and to be installed on a predetermined installation body,wherein a positional alignment mark to serve as a positional referenceof the photodetecting element is formed on the other surface of thephotodetecting element, a window portion to expose the positionalalignment mark is formed on the wiring board, and the base has apositioning portion positioned with respect to the positional alignmentmark exposed from the window portion, and a fitting portion positionedwith respect to the positioning portion and to be fitted with theinstallation body.

In this photodetecting device, the positional alignment mark to serve asa positional reference of the photodetecting element is formed at theother surface side of the photodetecting element. Moreover, the base isprovided with the fitting portion to be fitted with the installationbody, and the fitting portion is accurately positionally aligned withrespect to the photodetecting element via the positioning portionpositioned with respect to the positional alignment mark exposed fromthe window portion of the wiring board. Accordingly, in thisphotodetecting device, when fitting the fitting portion with theinstallation body, the photodetecting element is accurately positionallyaligned with respect to the installation body. As a result, even when,for example, a 4-side buttable arrangement is adopted, thephotodetecting elements in the respective photodetecting devices can beaccurately aligned in positional relationship, so that thephotodetecting devices can be arranged at a high density.

Moreover, it is preferable that the positional alignment mark is formedat two sites or more so as to pass through a center line of thephotodetecting element, and the positioning portion is composed of oneside face of the base and one end portion in the side face. In thiscase, by aligning, with the line passing through the positionalalignment mark, the line of one side face of the base, thephotodetecting element and the base can be accurately angularly aligned.And, the photodetecting element and the base can be accuratelypositionally aligned based on relative distances between the positionalalignment marks and one end portion.

Moreover, it is preferable that the fitting portion is a pin protrudedto the other surface side of the base. In this case, providing, on theinstallation body, a recess portion corresponding to the pin makes itpossible to simply install the photodetecting device on the installationbody.

EFFECTS OF THE INVENTION

The photodetecting device according to the present invention canaccurately perform positional alignment of the photodetecting elementwith respect to the installation body. As a result, even when, forexample, a 4-side buttable arrangement is adopted, the photodetectingelements in the respective photodetecting devices can be accuratelypositioned in positional relationship, so that the photodetectingdevices can be arranged at a high density.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] A view showing a photodetecting section formed with aphotodetecting device according to an embodiment of the presentinvention loaded.

[FIG. 2] A perspective view of the photodetecting device.

[FIG. 3] A view of the photodetecting device observed from the frontsurface side.

[FIG. 4] A side view showing a part of the photodetecting device in asectioned manner.

[FIG. 5] An enlarged sectional view in the vicinity of a slit portion.

[FIG. 6] An enlarged view of the slit portion observed from the frontsurface side, with a lid portion removed.

[FIG. 7] A side view of the photodetecting device observed from one endside.

[FIG. 8] Views showing an assembly process of the photodetecting device.

DESCRIPTION OF REFERENCE NUMERALS AND SYMBOLS

2 . . . cold plate (installation body), 3 . . . photodetecting device,11 . . . photodetecting element, 12 . . . wiring board, 13 . . . Spinbase (base), 16 . . . CCD array (photodetecting section), 18A, 18B . . .positional alignment mark, 23 . . . slit portion (window portion), 24 .. . cutaway portion (window portion), 32 . . . threaded fitting pin(fitting portion), 33 . . . positioning portion, 34 . . . side face (oneside face), 35 . . . corner portion (one end portion), L . . . centerline.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a preferred embodiment of the photodetecting deviceaccording to the present invention will be described in detail withreference to the accompanying drawings.

FIG. 1 is a view showing a photodetecting section formed with aphotodetecting device according to an embodiment of the presentinvention loaded. Also, FIG. 2 is a perspective view of thephotodetecting device shown in FIG. 1, FIG. 3 is a view of the sameobserved from the front surface side, and FIG. 4 is a side view showinga part of the same in a sectioned manner.

As shown in FIG. 1, the photodetecting section 1 includes a thermalcontrol cold plate (installation body) 2 and a plurality ofphotodetecting devices 3, and is formed as, for example, aphotodetecting section 1 of a telescope for astronomical observation.The cold plate 2 is formed of, for example, copper in a disk shape, andis cooled to approximately −100° C. in a predetermined gas ambient whenthe telescope is used. On the surface of the cold plate 2, a pluralityof recess portions 4 corresponding to a threaded fitting pin 32 and aflexible PCB(Printed Circuit Board) 22 (see FIG. 2) of eachphotodetecting device 3 are provided.

The photodetecting devices 3 are each fixed to the cold plate 2 byfitting the threaded fitting pin 32 and the flexible PCB 22 into therecess portions 4 and screwing a nut 36 (see FIG. 2) on each threadedfitting pin 32 from the back side of the cold plate 2, and arranged in,for example, an 8×10 matrix. Such arrangement is called a 4-sidebuttable arrangement since four side faces of each photodetecting device3 face the side faces of adjacent photodetecting devices 3, and issuitable for providing the photodetecting section 1 with a large area byarranging the photodetecting devices 3 at a high density. Moreover, theinterval between the adjacent photodetecting devices 3 is provided asapproximately 100 μm, thereby preventing contact of the photodetectingdevices 3 with each other due to thermal expansion after cooling by thecold plate 2 is cancelled.

Next, description will be given of a configuration of the photodetectingdevice 3. Each photodetecting section 3, as shown in FIG. 2 to FIG. 4,includes a photodetecting element 11 that performs photodetection, awiring board 12 electrically connected to the photodetecting element 11,and a pin base 13 to be used for installation onto the cold plate 2. Thephotodetecting element 11 is a so-called Back-Thinned CCD (BT-CCD)having a thickness of approximately 200 μm, and is an element capable ofdetecting, at a high sensitivity, various types of energy beamsincluding ultraviolet rays, soft X-rays, and electron beams that aresusceptible to the effect of absorption by a semiconductor.

The back surface (one surface) side of the photodetecting element 11serves as a light-incident surface S (see FIG. 4), and at the frontsurface (the other surface) side of the photodetecting element 11, adetecting region 14 that detects light made incident from thelight-incident surface S and a first bonding pad region 15 to serve asan output terminal of the detecting region 14 are respectively formed(see FIG. 8( a)). In the detecting region 14, provided is a CCD array(photodetecting section) 16 where CCDs are arranged in, for example, a9×7 matrix, and in the first bonding pad region 15, provided is a firstbonding pad 17A electrically connected with each pixel of the CCD array16 by a predetermined pattern of aluminum wiring. The first bonding pads17A are arranged in a line along one end portion of the front surfaceside of the photodetecting element 11.

Further, as shown in FIG. 3 and FIG. 8( a), in both end portions of thefront surface of the photodetecting element 11, at a dead area part on afurther outer side than the detecting region 14, cross-shaped positionalalignment marks 18 (18A, 18B) are respectively provided so as to passthrough a center line L of the photodetecting element 11. The positionalalignment marks 18A, 18B are formed simultaneously with theabove-described aluminum wiring by, for example, aluminum sputtering,and used as positional references that indicate the center line L of thephotodetecting element 11.

The wiring board 12, as shown in FIG. 2 to FIG. 4, shows a rectangularshape having almost the same area as that of the photodetecting element11, and in an almost central part of the front surface side of thewiring board 12, a lead terminal 21 corresponding to each pixel of theCCD array 16 is disposed. The lead terminal 21 is, as shown in FIG. 2,connected to the flexible PCB (flexible printed circuit board) 22. Theflexible PCB 22 is connector-connected to a predetermined substrate (notshown) in the telescope through the recess portions 4 of the cold plate2.

On the other hand, as shown in FIG. 3, in one end portion and the otherend portion of the wiring board 12, a slit portion (window portion) anda cutaway portion (window portion) 24 are provided, respectively. Theslit portion 23 is formed in an oblong shape along one end portion ofthe wiring board 12, and the cutaway portion 24 is formed in asemicircular shape at almost the center of the other end portion of thewiring board 12. In addition, the wiring board 12 is, while beingpositioned so that the first bonding pad region 15 and the positionalalignment mark 18A are exposed from the slit portion 23 and thepositional alignment mark 18B is exposed from the cutaway portion 24,firmly fixed to the front surface side of the photodetecting element 11by, for example, die-bonding.

Moreover, as shown in FIG. 5 and FIG. 6, on the wiring board 12, in aregion on a further inner side than the region where the first bondingpad region 15 and the positional alignment mark 18A are exposed, a stepportion 25 is provided along the longitudinal direction of the slitportion 23. The step portion 25 has an installation face 25 a located ata further back surface side than the front surface of the wiring board12, and on the installation face 25 a, formed is a second bonding padregion 26 to serve as an input terminal of the wiring board 12. In thesecond bonding pad region 26, second bonding pads 17B corresponding tofirst bonding pads 17A are arranged in a line, and the first bondingpads 17A and the second bonding pads 17B are electrically connected bybonding wires 27, respectively. In addition, the second bonding pads 17Bare electrically connected to the lead terminals 21 by internal wiring(not shown) of the wiring board 12, respectively, and thus an outputsignal from the photodetecting element 11 is externally output via thelead terminal 21 and the flexible PCB 22.

Further, at almost the center of an edge being on one end side of thewiring board 12, a groove portion 28 extending along the center line L(see FIG. 3) is provided, and the wiring board 12 is attached with aceramic lid portion 29 from the front surface side of the slit portion23 in a manner blocking the groove portion 28. By attaching the lidportion 29, the first bonding pad portion 17A, the second bonding pads17B, and the bonding wires 27 are protected so as not to be externallyexposed, and in the side face on one end side of the photodetectingdevice 3, as shown in FIG. 5 and FIG. 7, an air vent 30 to communicatethe interior of the slit portion 23 with the exterior is formed.

The pin base 13 is, as shown in FIG. 2 to FIG. 4, formed of, forexample, aluminum nitride in a flat rectangular parallelepiped shape.The pin base 13 is provided on a surface of the wiring board 12 oppositeto the surface on the photodetecting element 11 side. The pin base 13 isformed at almost the center with a rectangular opening portion 31 toexpose the lead terminals 21 of the wiring board 12. Moreover, at thefront surface side of the pin base 13, provided is a threaded fittingpin (fitting portion) 32 made of, for example, titanium onto which a nut36 can be screwed. The threaded fitting pin 32 is protruded to theoutside from a surface of the pin base 13 opposite to the surface on thewiring board 12 side. A total of three threaded fitting pins 32 areprovided in a manner sandwiching the opening portion 31, that is, one atthe center of one end side of the pin base 13 and one each at positionsclose to both corner portions of the other end side of the pin base 13.

Here, of the side faces of the pin base 13, one side face 34 along thecenter line L of the photodetecting element 11 and a corner portion 35of one end side in the side face 34 serve as a positioning portion 33 ofthe pin base 13. The threaded fitting pins 32, which are attached at thefront surface side of the pin base 13, are centered so that relativedistances from the side face 34 and the corner portion 35 becomeaccurate, and positioned at a high accuracy with respect to thepositioning portion 33, respectively. Moreover, the pin base 13 isaccurately angularly aligned with respect to the photodetecting element11 by aligning, with the center line L passing through the positionalalignment marks 18A, 18B, the line of the side face 34 when the pin base13 is observed from the front surface side, and is accuratelypositionally aligned with respect to the photodetecting element 11 basedon relative distances between the positional alignment marks 18A and 18Band the corner portion 35. In this state, the pin base 13 is firmlyadhered to the front surface side of the wiring board 12 by, forexample, a thermosetting resin.

Then, description will be given of an assembling method of thephotodetecting device 3 having the above-described configuration.

When the photodetecting device 3 is assembled as the photodetectingsection 1 of a telescope, first, the photodetecting element 11 isprepared, and the photodetecting element 11 is arranged, as shown inFIG. 8( a), with the front surface side oriented upside so that thepositional alignment marks 18A, 18B are visible. Next, the wiring board12 is prepared, and, as shown in FIG. 8( b), while being positioned sothat the first bonding pad region 15 and the positional alignment mark18A are exposed from the slit portion 23 and the positional alignmentmark 18B is exposed from the cutaway portion 24, the wiring board 12 isfixed to the front surface side of the photodetecting element 11 bydie-bonding.

After the fixation of the wiring board 12 is completed, the pin base 13is prepared. At the front surface side of the pin base 13, the threadedfitting pins 32 are attached in advance while being accurately centeredwith respect to the positioning portion 33. Then, as shown in FIG. 8(c), so that the lead terminals 21 of the wiring board 12 are exposedfrom the opening portion 31 being at almost the center of the pin base13, the pin base 13 is laid over the front surface side of the wiringboard 12. At this time, the line of the side face 34 when the pin base13 is observed from the front surface side is aligned with the centerline L passing through the positional alignment marks 18A, 18B, of thephotodetecting element 11, exposed from the slit portion 23 and thecutaway portion 24 of the wiring board 12 to accurately angularly alignthe pin base 13 with respect to the photodetecting element 11. Moreover,based on relative distances between the positional alignment marks 18Aand 18B and the corner portion 35, the pin base 13 is accuratelypositionally aligned with respect to the photodetecting element 11.After performing the angular alignment and positional alignment withrespect to the photodetecting element 11, the pin base 13 is fixed tothe front surface side of the wiring board 12 by adhesion.

After the fixation of the pin base 13 is completed, the first bondingpads 17A and the second bonding pads 17B are electrically connected bywire bonding, respectively. After the wire bonding, the lid portion 29is attached from the front surface side of the slit portion 23 to hidethe first bonding pads 17A and the second bonding pads 17B, and the airvent 30 is formed in the side face on one end side of the photodetectingdevice 3. Moreover, the flexible PCB 22 is connected to the leadterminal 21 exposed from the opening portion 31 of the pin base 13.Thereby, the assembly of the photodetecting device 3 shown in FIG. 2 toFIG. 4 is completed.

Then, by fitting the threaded fitting pins 32 and the flexible PCB 22 ofthe photodetecting device 3 into the recess portions 4 of the cold plate2 and screwing the nut 36 on each threaded fitting pin 32 from the backside of the cold plate 2, the photodetecting device 3 is fixed to thecold plate 2. At this time, since the threaded fitting pin 32 has beenaccurately positionally aligned with the photodetecting element 11 viathe positioning portion 33 of the pin base 13, the photodetecting device3 is accurately positionally aligned with respect to the cold plate 2.In the following, by assembling a plurality of photodetecting devices 3by the same procedure and arranging the photodetecting devices 3 in amatrix on the cold plate 2, the photodetecting section 1 shown in FIG. 1is completed.

As has been described above, in the photodetecting device 3, thepositional alignment marks 18A, 18B to serve as positional references ofthe photodetecting element 11 are formed at the front surface side ofthe photodetecting element 11. Moreover, the pin base 13 is providedwith the threaded fitting pin 32 to be fitted with the cold plate 2, andthe threaded fitting pin 32 is accurately positionally aligned withrespect to the photodetecting element 11 via the positioning portion 33positioned with respect to the positional alignment marks 18A, 18Bexposed from the slit portion 23 and the cutaway portion 24 of thewiring board 12. Accordingly, in the photodetecting device 3, by onlyfitting the threaded fitting pin 32 with the recess portion 4 of thecold plate 2, the photodetecting element 11 is accurately positionallyaligned with respect to the cold plate 2. As a result, in the 4-sidebuttable arrangement, the photodetecting elements 11, 11 in adjacentphotodetecting devices 3, 3 can be accurately aligned in positionalrelationship, so that it becomes possible to arrange the respectivephotodetecting devices 3 at a high density.

Moreover, in the photodetecting device 3, the positional alignment marks18A, 18B are formed so as to pass through the center line L of thephotodetecting element 11, and the positioning portion 33 is composed ofthe side face 34 of the pin base 13 and the corner portion 35 in theside face 34. Therefore, by aligning, with the center line L passingthrough the positional alignment marks 18A, 18B, the line of the sideface 34 when the pin base 13 is observed from the front surface side,the photodetecting element 11 and the pin base 13 can be accuratelyangularly aligned, and the photodetecting element 11 and the pin base 13can be accurately positionally aligned based on relative distancesbetween the positional alignment marks 18A and 18B and the cornerportion 35.

Further, in the photodetecting device 3, the second bonding pads 17B areformed, of the wiring board 12, in the region on a further inner sidethan the first bonding pad region 15. Due to such a configuration, inthe photodetecting device 3, a forming space for wire bonding can belocated at the inside of the photodetecting element 11, so that itbecomes possible to make the wiring board 12 and the photodetectingelement 11 almost equal in size. As a result, in the photodetectingdevice 3, the area that the photodetecting element 11 occupies relativeto the photodetecting device 3 can be sufficiently secured, and in thecase of a buttable arrangement of the photodetecting devices 3 on thecold plate 2, the interval between the photodetecting elements 11, 11 ofthe adjacent photodetecting devices 3, 3 can be sufficiently reduced, sothat minimization of the non-sensitive region can be realized. Moreover,by providing the second bonding pad region 26 on the installation face25 a of the step portion 25, the bonding wires 27 can be prevented fromprotruding to the front side of the wiring board 12. This allows, whenarranging the photodetecting devices 3 on the cold plate 2, protectingthe bonding wires 27 from disconnection etc. Further, since there issome thickness left at the forming part of the second bonding pads 17B,the strength of the bonding pads 17B when performing wire bonding canalso be secured.

The wiring board 12 is attached with the lid portion 29 from the frontsurface side of the slit portion 23 so that the first bonding pads 17A,the second bonding pads 17B, and the bonding wires 27 are protected soas not to be externally exposed, and the air vent 30 to communicate theinterior of the slit portion 23 with the exterior is formed. By thusprotecting the wire bonding part of the photodetecting element 11 andthe wiring board 12, disconnection etc., of the bonding wires 27 whenarranging the photodetecting device 3 on the cold plate 2 can beprevented. Moreover, by a formation of the air vent 30, the interior andthe exterior of the slit portion 23 can be maintained at an equalpressure even after the lid portion 29 is attached, and thus even whencooling or cancellation of the cooling is performed by the cold plate 2before and after use of the photodetecting section 1, deformation andbreakage of the photodetecting device 3 due to a contraction/expansionof the gas in the slit portion 23 can be suppressed.

The present invention is by no means limited to the above-mentionedembodiment. For example, in the embodiment described above, thephotodetecting section 1 has been formed by a 4-side buttablearrangement of the photodetecting devices 3 on the cold plate 2,however, by arranging the photodetecting devices 3 in two lines, a3-side buttable arrangement may be adopted where 3 side faces of thephotodetecting device 3 face the side faces of adjacent photodetectingelements 11.

Moreover, in the embodiment described above, on the pin base 13, oneside face 34 along the center line L of the photodetecting element 11and the corner portion 35 of one end side in the side face 34 have beenprovided as the positioning portion 33, however, one side faceorthogonal to the center line L of the photodetecting element 11 and acorner portion of one end side in the side face may be provided as thepositioning portion 33. Further, in the embodiment described above, thegroove portion 28 to form the air vent 30 has been provided at almostthe center of an edge being on one end side of the wiring board 12,however, such a groove portion 28 may be formed at the lid portion 29side, and may be formed at both the slit portion 23 and the lid portion29.

Further, in the embodiment described above, an output signal from thephotodetecting element 11 is externally output via the lead terminal 21and the flexible PCB 22, however, the present invention is not limitedthereto, and, for example, a connector to be fitted with the leadterminal 21 may be fitted from the opening portion of the pin base 13.Moreover, the cutaway portion 24 has been provided in a semicircularshape, however, this may, without limitation thereto, be in, forexample, an oblong shape. Moreover, when electrically connecting thefirst bonding pads 17A and the second bonding pads 17B by wire bonding,respectively, the wire bonding may be either a forward bonding or areverse bonding. Moreover, although the recess portions 4 have beenrecess portions, the recess portions 4 may be a plurality of holeportions that allow the threaded fitting pins 32 to be fitted thereintoand the flexible PCB 22 to pass therethrough.

1. A photodetecting device comprising: a photodetecting element thatdetects light made incident from one surface by a photodetecting sectionbeing on a side of the other surface; a wiring board provided at theother side of the photodetecting element and electrically connected withthe photodetecting section; and a base provided at the other side of thewiring board and to be installed on a predetermined installation body,wherein a positional alignment mark to serve as a positional referenceof the photodetecting element is formed on the other surface of thephotodetecting element, a window portion to expose the positionalalignment mark is formed on the wiring board, and the base has apositioning portion positioned with respect to the positional alignmentmark exposed from the window portion, and a fitting portion positionedwith respect to the positioning portion and to be fitted with theinstallation body.
 2. The photodetecting device according to claim 1,wherein the positional alignment mark is formed at two sites or more soas to pass through a center line of the photodetecting element, and thepositioning portion is composed of one side face of the base and one endportion in the side face.
 3. The photodetecting device according toclaim 1, wherein the fitting portion is a pin protruded to the othersurface side of the base.